PCD Percussion Drill Bit

ABSTRACT

An insert for a percussion drill bit for drilling a hole in rock comprises a cylindrical portion and domed cutting surface. The domed cutting surface that comprises polycrystalline diamond has a tip radius that is between 0.3 and 0.4 times that of the diameter of the cylindrical portion. The diameter of the cylindrical portion is preferably greater than the gauge diameter of hole multiplied by 0.2.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of non-provisional of U.S.application Ser. No. 12/273,700, filed Nov. 19, 2008, which claimspriority to provisional application Ser. No. 61/022,614, filed Jan. 22,2008, the entire disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to rock drill bits, and moreparticularly to rotary percussion drill bits having PCD insertsconstructed and arranged for improved performance and duration of thedrill bit in rock crushing and boring operations.

As used in the following disclosure and claims, the term“polycrystalline diamond” and/or its abbreviation “PCD” refers to amaterial formed of diamond crystals fused or sintered under highpressure and temperature into a predetermined layer or shape. The PCDmaterial is permanently bonded to a substrate of tungsten carbide in acobalt binder or like carbide matrix, also known in the art as“precemented carbide” to form a PCD insert. Also, as used herein, theterm “high density ceramic” or its abbreviation “HCD” refers to a miningtool having an abrasive working insert embodying a PCD layer.

2. Description of the Prior Art

The three basic ways of drilling bores in rock and earthen formationsare rotary, percussion (or impact), and rotary percussion (or rotaryimpact). Rotary percussion drilling is typically carried out by drivingthe drill bit into the rock work surface in a reciprocating manner at astriking or impact force of about 300-500 ft/lbs and also rotating thebit at about 250-300 rpm during drilling. The impact frequency is aboutsix (6) blows for each one (1) revolution. Using pneumatic power, thisequates to about 2100-2200 blows per minute; and a much higher impactfrequency of 7000 to 8000 striking blows per minute if using hydraulicpower. Thus, rotary percussion drilling is carried out byreciprocatingly driving the drill bit to crack and crush the rock androtating the bit to cut away and remove the crushed rock from thedeveloping bore hole.

A principal problem encountered in using prior art percussion drill bits(as in rotary cutting tools), is the rapid wear and high cost ofcontinual replacement along with machine down-time for changeover orreplacement of these inefficient bits coupled with the hazardous safetyrisks involved in hammering off the worn bits for replacement with newones. Typically prior art percussion drill bits are made with tungstencarbide inserts because it is a cheap and easily worked material, butsuch tools result in rapid failure due to wear and breakage. This hasled to drill bit redesign using more and bigger tungsten carbideinserts, which in turn generally generates higher dust levels and otherhealth problems.

SUMMARY OF THE INVENTION

One aspect of the invention is embodied in a percussion drill bit fordrilling bore holes in hard rock (minerals) which comprises a steel bodyhaving a working front head portion and a rearward shank portion forconnection to an impact driving force, the head portion having a frontfacing central zone and plural side wing zones extending radially fromthe central zone and spaced apart at the outer circumferential edgesthereof by grooves in the outer wall of the front head portion, firstgauge-cutting PCD inserts are secured in at least two of said side wingzones of the steel body and are constructed and arranged to extendforwardly and outwardly at an angle to the axis of the bit and beoperable for forming the bore hole, at least one second PCD insert isnon-axially secured in the central zone and projects forwardly of thefirst PCD inserts and is operable for impact at the core area of thebore hole to pilot the boring effort of the first PCD inserts.

In another aspect of the invention the head portion of the steel body isarmored with a hard cladding material tougher than the steel body tothereby reduce outer body wear at the side wing zones and to therebyprolong the PCD insert integrity and provide a substantially longerdrill bit life.

In yet another aspect of the invention, an insert for a percussion drillbit comprises a cylindrical portion and a domed cutting surface. Thecylindrical portion extends along an axis and has a diameter about theaxis. The domed cutting surface forms an axial end of the insert andcomprises polycrystalline diamond. The cutting surface has a tip radiuswhere the axis intersects the cutting surface. The tip radius and thediameter define a tip radius-to-diameter ratio. The tipradius-to-diameter ratio being is between 0.3 and 0.4.

In another aspect of the invention, a percussion drill bit is configuredand adapted to drill a hole in rock and comprises an insert. The inserthas a cylindrical portion and a domed cutting surface. The cylindricalportion extends along an axis and has a diameter about the axis. Thedomed cutting surface forms an axial end of the insert and comprisespolycrystalline diamond. The cutting surface has a tip radius where theaxis intersects the cutting surface. The tip radius and the diameterdefine a tip radius-to-diameter ratio. The tip radius-to-diameter ratiois between 0.3 and 0.4.

In still another aspect of the invention, a percussion drill bit isconfigured and adapted to drill a hole in rock of a given diameter. Thedrill bit comprises a body having shaft and head portions. The drill bitalso comprises at least one insert. The insert comprises a domed cuttingsurface that comprises polycrystalline diamond. The insert is rigidlyattached to the head portion of the drill bit. The insert furthercomprises a cylindrical portion having a diameter. The diameter of thecylindrical portion is greater than the diameter of hole multiplied by0.2.

These and other objects and advantages of the invention will become moreapparent from the drawing figures and the following description of thepreferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings which form a part of the specification andwherein like numerals refer to like parts wherever they occur:

FIG. 1 is a perspective view of a first embodiment of a percussion drillbit according to the invention;

FIG. 2 is a side elevational view of the first embodiment, partly brokenaway to show a PCD insert socket;

FIG. 3 is another side elevational view, as rotated 90° from the FIG. 2position, and broken away to show flushing fluid distribution;

FIG. 4 is a top plan view of the first embodiment;

FIG. 5 is a cross-sectional view taken substantially along line 5-5 ofFIG. 4;

FIG. 6 is a greatly enlarged diagrammatic and fragmentary viewillustrating the geometry of the working head portion of the firstembodiment;

FIG. 7 is a side elevational view of a second embodiment of theinvention with portions broken away to show side wall cladding; and

FIG. 8 is a section similar to FIG. 5 and showing a metal cladding ofthe head portion front face.

FIG. 9 is a side view of an embodiment of a PCD insert for use inpercussion drill bits, with the PCD coating represented by the diamondpattern.

FIG. 10 is a top plan view of percussion drill bit that comprises thePCD insert shown in FIG. 9

FIG. 11 is cross-sectional view of the drill bit shown in FIG. 10 takenabout the line 11-11 of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-6 show a first embodiment of a percussion rock drill bit of thepresent invention, generally designated 10. The drill bit includes asteel body 12 having a working head portion 14 and a rearward shankportion 16 with a common central axis “a-a” (FIG. 6). The shank portion16 has a central bore 20 with an internal rope thread 21 for threadedconnection to a hammer driven drill string apparatus (not shown). Thecentral bore 20 connects to three flushing channels 22 constructed andarranged to direct flushing and cooling fluid through the head portion14 and around the front facing surface 23 thereof. The front surface isgenerally perpendicular to the central axis “a-a” (as shown by referenceline “b-b” in FIG. 6).

The circumference of the front facing head portion area is larger thanthe circumference of the shank portion 16 whereby the outer side wall 24of the head portion 14 tapers inwardly from the front circumference downto the shank portion 16 about 8° (as shown in FIG. 6). It will beunderstood that the taper may be other than 8° within the scope of thepresent invention. The head portion 14 is provided with three verticaland elongate grooves or channels 25 that are symmetrically spaced aroundthe circumference and extend vertically toward the shank portion 16 andwhich define therebetween three symmetrically spaced wing zones 27. Itwill be clear that these wedge-shaped grooves 25 are constructed toreceive the flushing fluid ported from the passageways 22 and channel ittoward the working front face (23) of the head portion 14 as well asproviding a flow path for removing the rock chippings (not shown) as thebore hole is being formed.

The head portion 14 is provided with three first or primarygauge-cutting PCD inserts 30 symmetrically spaced from each other andsecured in primary sockets 38 into the wing zones 27. The head portion14 also is provided with second or secondary PCD inserts 31 constructedand arranged as core-cutters in a central zone 33 of the front face(23). Three such second PCD inserts are shown in the preferredembodiment of FIGS. 1-6, and these are asymmetrically and non-axiallyarranged in secondary sockets 45 in the central zone 33 at the front ofthe head portion 14. The circumferential area 35 of the front face ofthe tool extending radially outwardly from around the central zone 33 issloped axially rearwardly (or downwardly in the drawings) at an angle ofabout 15° to 35°, and preferably about 22° to 26° (see “h” in FIG. 6).The head portion 14 is provided with the three primary sockets 37 formedin each of the wing zones 27 and extending into the steel body 12 onaxes substantially perpendicular to the slope of the wing zone surface35, and these sockets 37 are slightly smaller (i.e., about 0.002 inch)than the base diameter of the first PCD inserts 30 whereby the press-fitof the inserts under about 5 tons of force provides a secure seating ofthe inserts 30 in the sockets 37 through it will be noted that the firstgauge-cutting PCD inserts 30 in the first embodiment are larger than thesecond core-breaking PCD inserts 31. The first PCD inserts 30 willtypically have a main body of tungsten carbide with a cylindrical basesection 42 and a domed working end 39 capped with a parabolic orbullet-shaped domed crown 40 of PCD material (see FIG. 5). Whenassembled the base section 42 is deeply seated in the socket 37 of eachwing zone 35 and the cylindrical wall extends beyond the sloping headportion surface about 1/16 inch (at 41) so that the gauge-cutting PCDcrown caps 40 are precisely set at a predetermined position (see “e-e”of FIG. 6) in front of the front face “b-b” of the head portion 14.

The secondary core-cutting PCD inserts 31 have essentially the sameconfiguration as the first PCD inserts 30, although they have a smallerdiameter in the preferred first embodiment. The coring PCD inserts 31are set in sockets 45 formed in the central zone 33 of the front face(23) and are non-symmetrically and non-axially arranged to impactagainst different adjacent core areas as the bore hole is being formed.The secondary PCD inserts 31 are also set to extend forwardly of thefront face (23), but in an axial direction and to a precise spaceddistance (plane “d-d” in FIG. 6) that is beyond the plane “e-e” of thegauge-cutting PCD inserts 30. As shown in FIGS. 1-3, the central zone 33may be formed as an elevated or raised platform having a side wall 43.Thus, in operation, it will be clear that the core-cutting PCD inserts31 initiate or pilot the bore hole formation by breaking a smallercentral core area thereof followed by the gauge-cutting action of thefirst PCD inserts 30 to complete the full bore hole drilling. Clearlythe flushing fluid carries away the loose chippings as the hole isformed as well as cools the diamond inserts 30, 31 to preventoverheating thereof. It will be understood that a wide variance ofnon-symmetrical coring insert arrangements can be made, and that havinga side wall 43 larger diameter inserts 31 may be used on larger sizedboring tools 10.

The geometry of the PCD inserts 30 and 31 in their sockets 37 and 45 canbest be seen in FIGS. 5 and 6. This geometry contributes to theintegrity of the drill-bit, 110 and prolongs its useful life; andincludes the angular relationship between the primary sockets 37 and thesecondary sockets 45 and the depth thereof in the head portion 14 of thedrill bit. As shown, the primary sockets 37 extend deepest (at 38) intothe tool body 12. The primary PCD inserts 30, extend outwardly at anangle to the axis of the drill bit but are arranged to produce areaction force vector in an axial direction to push these primaryinserts 30 more firmly into these sockets 37. The secondary sockets 47for the core-cutting PCD inserts 31 extend in an axial direction, butthe bottoms 46 thereof are above the deeper primary sockets 37 and haveno negative influence thereon. It may also be noted that the sphericalcutting face of the respective PCD inserts distribute impact forcesthrough the insert bodies, and further that the PCD layer itself doesnot wear out.

As shown best in FIGS. 1 and 4, the central zone 33 is shown as acircular area that is axially centered and is also shown as a raisedplatform having a side wall 43 of a minor dimension. The distance thatthe contact point of the core-breaking inserts extends forwardly of thecrown of the gauge-cutting inserts is at least as large as the platformelevation. It will be understood that the central zone 33 of the frontface 23 may be a different shape such as a triangle, trapezoid orpentagon that will help to define selected non-asymmetrical locationsfor orientation of multiple cone-cutting inserts 31 without interferencewith the seating sites (primary sockets 37) for the gauge-cuttinginserts 30. In other words, the raised platform 43 facilitates thelocation of secondary sockets in an axial direction away from theangularly related sockets 37 for the outer PCD inserts but withoutdirect interference or compromising their structural integrity or thepress-fit strength thereof.

Referring to a second form of the invention shown in FIGS. 7 and 8, thesteel body 112 at the head portion 114 of the drill bit 110 can bestrengthened to better obviate erosion and wear of the head portionsurface areas if reinforced by a harder metal cladding 150. It will beappreciated that parts of the drill bit 110 corresponding to drill bit10 will are given the same reference numeral, plus “100.” The use ofexotic steels alloyed with chromium carbide or vanadium carbide wouldprovide the toughest steel bodies for percussion tools, but at greatexpense. The present invention contemplates bonding a chromium orchromium alloy jacket 150 over the entire head portion 114 of the tool110. This chromium cladding layer 150 would have a thickness in therange of 0.005 to 0.010 inches and be tempered to a Rockwell hardness ofat least 60 Rc and preferably 65-68 Rc. In manufacturing the drill tool110, the sockets 137 and 145 for the first and second PCD inserts 130and 131 will be formed after cladding process is completed.

An embodiment of a PCD insert in accordance with another aspect of theinvention is shown in FIG. 9. This insert 200 comprises a cylindricalportion 202 and a domed cutting surface 204. The cylindrical portion 202extends along an axis “c-c” and has a diameter “D1” about that axis. Thedomed cutting surface 204 forms an axial end of the insert and comprisespolycrystalline diamond 206. The domed cutting surface 204 has a radius“R1” at its tip or apex (i.e. where the axis intersects the cuttingsurface). This tip radius and the diameter of the cylindrical portion202 define a tip radius-to-diameter ratio. That ratio is preferablybetween 0.3 and 0.4, and more preferably between 0.33 and 0.35 Forexample, the insert 200 may have a tip radius of 0.15 inches and adiameter of 0.44 inches. Preferably the domed cutting surface 204 of theinsert 200 comprises a first surface portion 208 that has a constantradius equal to the tip radius, a second surface portion 210 that has ashape defined by an arc of a constant radius “R2” revolved about theaxis of the insert, and a third surface portion 212 that isfrustoconical in shape. The constant radius arc that defines the shapeof the second surface portion 210 preferably has a radius that isgreater than the tip radius. For example, the radius of the arc may be0.70 inches. The second surface portion 210 preferably tangentiallymeets the first surface portion 208 and the third surface portion 212.The third surface portion 212 extends from the cylindrical portion 202to the second surface portion 210.

A head-on view of a percussion drill bit 214 that comprises the insert200 shown in FIG. 9 is shown in FIGS. 10 and 11. The drill bit 214comprises a shaft portion 216 and a head portion 218. The head portion218 comprises a central portion 220 and a pair of wing portions 222. Thewing portions 222 protrude radially from the head portion 218 inopposite directions (left and right as shown). As shown, the drill bit214 comprises six of the PCD inserts 200, and many of the features ofthe other drill bit embodiments described above. Each of the wingportions 222 comprises two of the inserts 200 protruding therefrom.Those inserts 200 constitute the gauge-cutting inserts and also overlapthe central portion 220 of the head portion 218 of the drill bit 214 inmanner such that they also protrude from the central portion. The tworemaining inserts 200 protrude axially from the head portion 218 andconstitute the core-cutting inserts. These two core-cutting inserts 200are preferably non-symmetrically spaced form the center axis. This drillbit 214 is preferably configured to cut a hole having a 2.0 inch borediameter. The diameter of the cylindrical portion 202 of each of thegauge-cutting inserts 200 is preferably greater than the bore diameterof hole multiplied by 0.2. For example, with a 2.0 inch bore drill bit214, the diameter of the cylindrical portion is preferably 0.44, makingit 0.22 times the diameter of the gauge diameter of the hole.Preferably, the tip of each insert 200 extends approximately 0.33 inchesfrom the head portion 218 of the drill bit 214. The drill bit 214 alsopreferably comprises a plurality of water holes 224 for clearing crushedrock. Some of the water holes 224 exit from the central portion 220 ofthe drill bit 214, and some from the flutes 226 that lie between thewing portions 222 of the drill bit.

When in use, the drill bit 214 thrust pressure is preferably kept belowa maximum value depending upon the gauge diameter of the drill bit. Fora bit having a gauge diameter in the range of 1.75 inches to 2.5 inches,the thrust pressure on the drill bit is preferably maintained at orbelow 363 psi while drilling, and more preferably at or below 290 psi.For a bit having a gauge diameter in the range of 1.375 inches to 1.625inches, the thrust pressure on the drill bit is preferably maintained ator below 290 psi while drilling, and more preferably at or below 218psi. Using the drill bit in this manner, the drill bit will cut onaverage approximately 35% faster than a new carbide drill bit operatedat higher thrust pressures. Moreover, the drill bit will cut on averageapproximately 50% faster than a worn carbide drill bit operated in aconventional manner. Unlike conventional carbide bits, the insert of thedrill wear several orders of magnitude less during use. Moreover, unlikeother PCD drill bits, the drill bits of the present invention do notchip when used as described above. As such, the performance advantagesachieved by the drill bits of the present invention far outweigh thehigher cost of such bits as compared to conventional carbide drill bits.

Although the present invention has been described with reference to thepreferred embodiments, it will be apparent to those skilled in the artthat changes and modifications not specifically disclosed can be madewithout departing from the spirit and scope of the invention as definedin the appended claims.

1. An insert for a percussion drill bit comprising: a cylindricalportion that extends along an axis, the cylindrical portion having adiameter about the axis; a domed cutting surface that forms an axial endof the insert, the cutting surface comprising polycrystalline diamond,the cutting surface having a tip radius where the axis intersects thecutting surface, the tip radius and the diameter defining a tipradius-to-diameter ratio, the tip radius-to-diameter ratio being between0.3 and 0.4.
 2. An insert in accordance with claim 1 wherein the cuttingsurface comprises a first surface portion having a constant radius equalto the tip radius, a second surface portion having a shape defined by aconstant radius arc revolved about the axis, and a third surface portionthat is frustoconical in shape, the constant radius arc that defines theshape of the second surface portion has a radius that is greater thanthe tip radius, and the third surface portion extends from thecylindrical portion to the second surface portion.
 3. An insert inaccordance with claim 1 wherein the diameter of the cylindrical portionis greater than 0.40 inches and less than 0.48 inches.
 4. An insert inaccordance with claim 3 wherein the tip radius is greater than 0.1inches and less than 0.2 inches.
 5. An insert in accordance with claim 4wherein the tip radius is greater than 0.14 inches and less than 0.16inches.
 6. An insert in accordance with claim 1 wherein the tipradius-to-diameter ratio is between 0.33 and 0.35.
 7. A percussion drillbit configured and adapted to drill a hole in rock, the hole having adiameter, the drill bit comprising: a body having shaft and headportions; at least one insert, the insert comprising a domed cuttingsurface that comprises polycrystalline diamond, the insert being rigidlyattached to the head portion, the insert comprising a cylindricalportion having a diameter, the diameter of the cylindrical portion beinggreater than the diameter of hole multiplied by 0.2.
 8. A percussiondrill bit in accordance with claim 7 wherein the head portion comprisestwo wings and a central portion, the two wings protrude in radiallyopposite directions from the central portion, the drill bit comprisessix of the inserts, each wing has two of the inserts protrudingtherefrom, and the central portion has two of the inserts protrudingtherefrom.
 9. A percussion drill bit in accordance with claim 8 whereinthe inserts protrude from the head portion by at least 0.30 inches. 10.A percussion drill bit in accordance with claim 8 wherein each of theinserts that protrude from the wings also protrudes overlap the centralportion of the head portion and also protrude from the central portion.11. A percussion drill bit in accordance with claim 7 wherein thediameter of the cylindrical portion defines an axis, the cutting surfacehas a tip radius where the axis intersects the cutting surface, the tipradius and the diameter of the cylindrical portion define a tipradius-to-diameter ratio, and the tip radius-to-diameter ratio isbetween 0.3 and 0.4.
 12. A percussion drill bit in accordance with claim11 wherein the tip radius is greater than 0.14 inches and less than 0.16inches.
 13. A percussion drill bit in accordance with claim 11 whereinthe tip radius-to-diameter ratio is between 0.33 and 0.35.
 14. Apercussion drill bit in accordance with claim 11 wherein the cuttingsurface comprises a first surface portion having a constant radius equalto the tip radius, a second surface portion having a shape defined by aconstant radius arc revolved about the axis, and a third surface portionthat is frustoconical in shape, the constant radius arc that defines theshape of the second surface portion has a radius that is greater thanthe tip radius, and the third surface extends from the cylindricalportion to the second surface portion.
 15. A percussion drill bit inaccordance with claim 11 wherein the diameter of the cylindrical portionis greater than 0.40 inches and less than 0.48 inches.
 16. A percussiondrill bit in accordance with claim 15 wherein the tip radius is greaterthan 0.1 inches and less than 0.2 inches.
 17. A percussion drill bitconfigured and adapted to drill a hole in rock, the percussion drill bitcomprising: an insert, the insert having a cylindrical portion thatextends along an axis, the cylindrical portion having a diameter aboutthe axis, the insert also having a domed cutting surface that forms anaxial end of the insert, the cutting surface comprising polycrystallinediamond, the cutting surface having a tip radius where the axisintersects the cutting surface, the tip radius and the diameter defininga tip radius-to-diameter ratio, the tip radius-to-diameter ratio beingbetween 0.3 and 0.4.
 18. A method of drilling a hole in rock using thepercussion drill bit of claim 17, the hole having a bore diameter in therange of 1.75 inches to 2.5 inches, the method comprising maintaining athrust pressure on the drill bit below 363 psi while drilling.
 19. Amethod of drilling a hole in rock using the percussion drill bit ofclaim 17, the hole having a bore diameter in the range of 1.375 inchesto 1.625 inches, the method comprising maintaining a thrust pressure onthe drill bit below 291 psi while drilling.